Apparatus for direct smelting of zinc bearing compounds to produce metallic zinc

ABSTRACT

Apparatus for producing lead and zinc from concentrates of zinc and lead sulfides or oxides, including: a source of zinc ore and/or lead ore concentrates, iron bearing and carbon containing materials; metallic iron fines and iron oxide fines; carbonaceous reductant; fluxing agent; and a binder; a mixer for forming a mixture from said concentrates and other materials; an agglomerator communicating with the mixer for forming agglomerates from the mixture; a melting furnace for melting the mixture and vaporizing lead and zinc; a pressure sealed feed system communicating with the agglomerator and the melting furnace for introducing agglomerates to the melting furnace; a pressure sealed chamber surrounding the melting furnace; a water-cooled condenser for receiving the vaporized metal and cooling and condensing the metal vapors to liquid metal; a tapping device communicating with the condenser for removing the liquid metal; and associated devices for separating the zinc and lead and recovering the lead and zinc metal separately.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of the followingapplications:

PCT Application PCT/US2008/010122 filed: 12 Aug. 2008, U.S. ProvisionalPatent Application Ser. No. 60/967,347, filed 4 Sep. 2007;

PCT Application PCT\US 2008\010124, filed: 12 Aug. 2008, U.S.Provisional Patent Application Ser. No. 60/997,616, filed: 4 Oct. 2007

PCT Application PCT\US 2008\010123, filed 12 Aug. 2008, and U.S.Provisional Patent Application Ser. No. 61/126,915, filed 8 May 2008.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producingmetallic zinc or lead by direct smelting of zinc or lead bearingcompounds which generally incorporate zinc and/or lead in sulfideand/oxide form (ZnS and/or ZnO, PbS and/or PbO) therein.

SUMMARY OF THE INVENTION

Zinc bearing compounds, principally ZnS or ZnSO₄, but also ZnO andmaterials containing zinc oxide, such as electric arc furnace dust(EAFD), are cold briquetted to form compact agglomerates containing acarbonaceous material such as coal, coke, petcoke, char, etc., ironoxide (either already contained in the ore or added separately as ironore fines, mill scale, metalized iron fines, etc., to the mix), fluxessuch as lime, silica, spar, etc., and binder. An excess amount of carbonis present in the agglomerate, not only to react with the zinccompounds, but also to reduce the iron oxide, manganese oxide, leadoxide, cadmium oxide, etc., so that the melter atmosphere ispredominantly CO with some liberated H₂ from the volatilization of thecoal. The oxygen contained in the iron oxide is free to react with thezinc sulfide to form ZnO, or the zinc sulfide can sublime upon reachinghigh temperatures to liberate zinc vapor. Sulfur in the system is freeto combine with the liquid iron to form liquid FeS or dissolved sulfurin iron.

OBJECTS OF THE INVENTION

The principal object of the present invention is to provide an effectivemethod and apparatus for recovering zinc and lead from concentrates ofsulfides and oxides.

Another object of the invention is to provide a means for producing allthe required electricity to accommodate the process and operate theplant in such manner as to be electricity self sufficient.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects will become more readily apparent byreferring to the following detailed description and the appendeddrawing, in which:

FIG. 1 is a schematic flowsheet of the process for recovering zinc andlead from concentrates of sulfides and oxides according to theinvention.

FIG. 2 is a schematic flowsheet for producing electricity from theoff-gases from the invented process.

FIG. 3 is a schematic flowsheet showing an alternative method forrecovering zinc and lead in which feed materials are preheated with orwithout agglomeration, then fed to the melting furnace.

The reference numerals in the figures refer to the following items:

-   10—lead ore and/or zinc ore concentrate—100% passing 10 mesh Tyler    Standard (1.70 mm), preferably 100% passing 100 mesh Tyler Standard    (150 microns)-   12—metallic iron fines, and iron oxide fines—100% minus 25 mm,    preferably 100% passing 10 mesh-   14—prepared reductant, such as coal, coke, petroleum coke, char,    etc., 100% passing 25 mm, preferably 100% passing 100 mesh Tyler    Standard (150 microns)-   16—fluxing agents—CaO, MgO, CaF₂, Al₂O₃, SiO₂, etc—100% minus 25 mm-   18—binder such as cellulose, bentonite, molasses, starch—either    organic or inorganic-   20—recycled fines-   22—mixer-   24—briquetter/agglomerator (size 8 to 100 cc)-   26—water addition-   28—pelletizer—drum or disc type-   30—screens—dry or roller type-   32—greenball dryer (dries pellets to 1% moisture or less)-   34—agglomerate (briquette) curing/storage hoppers-   36—feed loss in weight system-   37—pressure sealed chamber-   38—electric melting furnace or melter>100° C.-   40—ladle(s) for liquid iron and iron sulfide-   42—slag addition for desulfurization-   44—pig iron caster-   45—pig iron-   46—slag ladle-   48—slag disposal/quench bunker-   50—melter off gas zinc and lead liquid condenser, water cooled-   52—cooling tower-   53—tapping ladle-   54—offgas indirect cooling exchanger-   56—offgas cooling scrubber/bag filter-   58—fan-   60—stack with combustion to convert CO & H₂ to CO₂ & H₂O-   62—high pressure compressor (300-350 psig)-   64—optional gas stream, sulfur removal system, such as Selexol-   66—high pressure gas accumulator tank-   68—gas turbine (exit gas temp 600-700 C)-   70—generator-   72—waste heat boiler heat exchanger-   74—high pressure steam turbine-   76—generator-   78—boiler closed circuit water conduit-   80—pump-   82—optional chiller upstream of gas sulfur removal system-   84—heater, direct or indirect rotary kiln type

DETAILED DESCRIPTION

Zinc ores appear in sulfide or sulfide and oxide form. Virtually allzinc smelting operations are predicated on first roasting the ore toliberate SO₂/SO₃ and convert ZnS to ZnO which is then reduced to produceZn vapor, which vapor is then condensed by lowering the temperature ofthe smelter offgas. Also, the smelter is operated so that the iron unitsare tapped out as quality pig iron, which necessitates certainrestraints on operation. In many cases the SO₂/SO₃ is recovered as H₂SO₄that is used to leach the primary ore. I have made thermodynamiccalculations examining the various processing routes and have discoveredthat if processing is oriented at direct smelting the ZnS in an electricmelter that has a strongly reducing environment created by feedingagglomerates that contain carbon (e.g., coal or other solid carbon) andkeeping the melter sealed against air ingress, then a different approachto zinc recovery can be taken.

In the present invention, the agglomerates also include some iron oxideand slag flux agents (CaO and MgO). During the course of heating in themelter, the ZnS is converted to Zn vapor directly or to ZnO and thenreduced to Zn vapor. The source of oxygen to make ZnO is provided by thereduction of the iron oxide (Fe₂O₃->FeO), and it is the FeO that reactswith the zinc sulfide. The zinc vapor is condensed from the exhaust gasby using conventional condenser technology, and the liberated sulfur istied up primarily by the liquid Fe in the form of liquid FeS or reactswith the CaO to form CaS, and is kept in the liquid state as FeS orslag. There is so little iron required in the invented process thatrecovering of pig iron is not important, instead liquid FeS is tapped.The zinc recovery drives the process economics.

As seen in FIG. 1, feed materials are introduced to mixer 22, the inputmaterials consisting of: lead ore and/or zinc ore concentrates 10, 100%of which pass 10 mesh Tyler Standard (1.70 mm), preferably 100% of whichpass 100 mesh, Tyler Standard (150 microns); metallic iron fines andiron oxide fines 12, 100% of which are minus 25 mm, preferably at least50% of which pass 10 mesh; prepared reductant 14, such as coal,petroleum coke, char, or other carbonaceous material, 100% of which areminus 25 mm, preferably 100% of which pass 10 mesh Tyler Standard (1.70mm); slag formers or fluxing agents 16, such as MgO, CaO, Al₂O₃, CaF₂(fluorspar) and SiO₂, 100% of which are minus 25 mm; an organic orinorganic binder 18, such as cellulose, bentonite, molasses, or starch;recycled fines 20, and water 26 as needed.

These materials are mixed in mixer 22, then formed into agglomerates inbriquetter/agglomerator 24, or in pelletizer 28 (such as a drum or disctype pelletizer), the agglomerates being in the form of uniformly sizedbriquettes or pellets, preferably about 8 cc to 100 cc in size. Theagglomerates are screened by sizer 30, such as a dry screen or a rollertype screen, the undersized material being returned to the agglomerator24 or to the mixer 22.

Screened pellets from pelletizer 28 are dried in a greenball dryer 32 to1% or less moisture content. The agglomerates are cured and/or stored inhoppers 34, then fed into an electric melting furnace 38 through apressure-sealed feed system 36, similar to a feed leg of a shaftfurnace, or through lock valves. The temperature of the electric furnacemelter is maintained in a sufficiently high range that it formsvaporized lead and zinc, which is removed as off gas, and condensed incondenser 50. The melter operating temperature is in the range of from100 C to 1650 C, preferably in the range of 1200 C to 1550 C. Theelectric furnace melter 38 operates normally under a slight positivepressure. The lead and zinc are tapped from the condenser 50. Differencein densities of liquid metals, particularly lead and zinc, allows theheavier (more dense) lead to be tapped first from a settling pot of thecondenser 50, followed by tapping of the lighter zinc to a tapping ladle53. This is done on an intermittent basis.

A mixture of iron and iron sulfide is removed from the melter intoladles 40 and may be cast into pigs 45 at pig caster 44, as shown.

Alternatively, material D1 exiting mixer 22 can be fed to a heater 84for the purpose of preheating the mixture to about 500 to 1200 C,devolatizing the reductant, and producing a preheated charge to electricfurnace melter 38. Pre-reduction of the iron oxide will occur to levelsranging from about 0 to 90%. Agglomerated material D2 can also bepreheated, if desired, prior to feeding the material to the melterthrough the pressure seal 37. The heater 84 can be an indirectly heatedrotary kiln, or a direct fired kiln, as shown, with off-gases beingrecycled. The heater 84 can be refractory lined, or it can be unlined,as desired.

Optionally one or more additional feed materials may be introducedthrough a pressure seal directly to the melter 38 as shown by dottedlines in FIG. 1, such additional materials being selected from a groupincluding metallic iron fines and iron oxide fines 12, 100% of which areminus 25 mm, preferably minus 10 mesh; prepared reductant 14, such ascoal, petroleum coke, or other carbonaceous material, 100% of which areminus 25 mm, preferably 100% of which pass 10 mesh, Tyler Standard (1.70mm), and slag formers or fluxing agents 16, such as MgO, CaO, Al₂O₃,CaF₂ (fluorspar) and SiO₂, 100% of which are minus 25 mm.

The operating parameters of the invented process are as follows:

Normal Range Maximum Lead Zinc Melter 1200-1550 C. 1650 C. MelterOff-Gas 500-1500 C. 1200-1650 C. Off-Gas from 300-700 C. <900 C. Zn—PbCondenser Melter Off-Gas 0-0.2″ H₂O gauge <15″ H₂O gauge Pressure GasAccumulator 100-350 psig Off-Gas Pressure Gas Turbine Combined 750-900C. <1000 C. Product Exit Temp.

Offgas exiting the condenser 50 is cleaned in a cooler/scrubber 56,which may include a bag filter, moved by fan 58 and compressed in highpressure compressor 62 and used as combustion fuel in gas turbine 68.Gas turbine 68 drives generator 70 to produce electricity, and sensibleheat contained in offgas exiting the gas turbine is recovered in a wasteheat recovery boiler system 72. The waste heat boiler system 72 steamcycle could be a “Kalina” cycle based on using 70% ammonia and 30% waterfor better range processing and heat recovery efficiency at lower gastemperatures. Ammonia/water boiling occurs over a range of temperaturesrather than at a specific temperature and pressure. Steam produced bythe waste heat boiler system 72 is then used to drive a steam turbine 74and generator 76 to produce additional electricity. One of the primeobjectives that is realized by the invention is to produce all therequired electricity to accommodate the process and operate the plant soas to be electricity self sufficient.

Waste off-gas from everywhere in the process is combusted in stack 60 toconvert carbon monoxide and hydrogen to carbon dioxide and water vapor.

Gas from the compressor 58 can be treated for sulfur removal in anoptional sulfur removal system 64, which may require an optional chiller82 upstream of the sulfur gas removal system.

SUMMARY OF THE ACHIEVEMENT OF THE OBJECTS OF THE INVENTION

From the foregoing, it is readily apparent that I have invented animproved method and apparatus for recovering zinc and lead fromconcentrates of sulfides and oxides more effectively than heretofore.

It is to be understood that the foregoing description and specificembodiments are merely illustrative of the best mode of the inventionand the principles thereof, and that various modifications and additionsmay be made to the apparatus by those skilled in the art, withoutdeparting from the spirit and scope of this invention.

1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled)
 5. (canceled) 6.(canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. Apparatusfor producing lead and zinc from concentrates of zinc and lead sulfidesor oxides, comprising: (a) a source of zinc ore and/or lead oreconcentrates, iron bearing and carbon containing materials; metalliciron fines and iron oxide fines; carbonaceous reductant; fluxing agent;and a binder; (b) a mixer for forming a mixture from said concentratesand other materials; © means communicating with said mixer for formingagglomerates from said mixture; (d) a melting furnace; (e) a pressuresealed feed system communicating with said agglomerating means and saidmelting furnace for introducing said agglomerates to said meltingfurnace; (f) a pressure sealed chamber surrounding said melting furnace;(g) means for maintaining a reducing atmosphere within said meltingfurnace; (h) means for vaporizing lead and zinc in the melting furnace;(I) means for removing the lead and zinc from the melting furnace invaporized form; (j) water-cooled condenser means for cooling andcondensing the metal vapors to liquid metal; (k) tapping meanscommunicating with said condenser for removing the liquid metal; and (l)means for separating the zinc and lead and recovering the lead and zincmetal separately.
 16. Apparatus according to claim 15, wherein the meansfor forming agglomerates is a pelletizer, briquetter, or agglomerator.17. Apparatus according to claim 15, wherein the means for separatingthe zinc and lead and recovering the lead and zinc metal separatelyincludes a settling pot associated with said condenser, said settlingpot having zinc tapping means directed to a zinc tapping ladle. 18.Apparatus according to claim 15, having a heater communicating with saidmixer for preheating the mixture and producing a preheated charge tosaid melting furnace.
 19. Apparatus according to claim 15, furthercomprising a cooler-scrubber communicating with said melting furnace forcleaning and cooling the off-gases removed from said melting furnace.20. Apparatus according to claim 19, further comprising a gas turbinecommunicating with said cooler-scrubber for receiving and utilizing thecleaned and cooled off-gases as combustion fuel.
 21. Apparatus accordingto claim 20, further comprising a generator associated with and drivenby said turbine.
 22. Apparatus according to claim 20, further comprisinga waste heat boiler associated with said turbine for recovering thesensible heat contained in off-gas exiting the said turbine, andproducing steam.
 23. Apparatus according to claim 22, furthercomprising: a steam turbine associated with said waste heat boilerdriven by the steam from said waste heat boiler, and an associatedgenerator driven by said steam turbine for producing additionalelectricity.